Hepatitis C virus (HCV) is a positive-sense single-stranded RNA virus belonging to the family Flaviviridae. HCV is the cause of non-A, non-B hepatitis (Kuo, G., et al., 1989, Science 244, 362-364), and when the HCV infection develops into chronic hepatitis, it can lead to liver cirrhosis or liver cancer with a high mortality rate (Saito, I., et al., 1990, Proc. Natl Acad. Sci. USA 87, 6547-6549). About 1 to 2% of the total population in the world is infected with hepatitis C virus. However, since HCV is present in the body with a very low titer, it is hard to diagnose HCV infection. Furthermore, an effective drug or vaccine for targeting HCV virus has not been developed yet.
Recently, a use of α-interferon that is partly effective against HCV-related diseases by suppressing HCV proliferation and co-administration of the α-interferon and ribavirin are available for treatment of HCV infection. However, it has been reported that effects of these methods vary among different virus strains and they remain to be effective for only 50% of the HCV-infected patients (Bartenschlager R, Frese M, Pietschmann T. Novel insights into hepatitis C virus replication and persistence. Adv Virus Res 2004, 63, 71-180).
When the viral components are targeted for HCV treatment, this often leads to the emergence of HCV escape mutants. Thus targeting host factors instead has emerged as an alternative strategy to HCV treatment.
MicroRNAs (miRNAs) are endogenous, small non-coding RNAs that function to repress cellular gene expression in a sequence-specific manner, generally through translational repression or degradation of target mRNAs (Chekulaeva M, Filipowicz W. Mechanisms of miRNA-mediated post-translational regulation in animal cells. Curr Opin Cell Biol 2009, 21, 452-460). MicroRNA 122 (miR-122) is the most abundant miRNA in the liver among others (Chang J., et al., miR-122, a mammalian liver-specific microRNA, is processed from her mRNA and may down-regulate the high affinity cationic amino acid transporter. RNA Biol 2004, 1, 106-113) and it is known to promote HCV replication by interacting with the 5′ untranslated region (UTR) of the viral genome (Jopling C L., et al., Modulation of hepatitis C virus RNA abundance by a liver-specific microRNA. Science 2005, 309, 1577-1581; Henke J I., et al., microRNA-122 stimulates translation of hepatitis C virus RNA. EMBO J 2008, 27, 3300-3310 etc.).
In the recent study, it has been reported that when the HCV-infected chimpanzees were treated with the antisense oligonucleotide against miR-122, HCV proliferation could be suppressed (Lanford R E., et al., Therapeutic silencing of microRNA-122 in primates with chronic hepatitis C virus infection. Science 2010, 327, 198-201). However, microRNA plays an important role in regulating the expression of a large number of genes involved in cellular physiological function including lipid metabolism (Krutzfeldt J., et al. Silencing of microRNAs in vivo with ‘anagomir’. Nature 2005, 438, 685-689). Therefore, the non-selective silencing of microRNA-122 independent of cell types is highly likely to cause side effects due to the gene modification of the genes that are critical for the cellular physiological activity.
Therefore, there is a high demand for the development of a silencing system that can inhibit the microRNA-122 activity selectively in HCV-replicating cells but not in normal liver cells.
In this regard, the present inventors have developed an aptazyme that is capable of releasing the antisense sequence to microRNA by specifically responding to the HCV RNA-encoding component in order to inhibit microRNA activity specifically in HCV-replicating cells, thereby completing the present invention.